This invention relates to fused cast refractories and more particularly relates to such refractories which are used for glass manufacture and particularly in the manufacture of alkaline earth borosilicate glass known as "E" glass which is used extensively in the production of glass fibers.
Fused cast refractories have been known and used for many years. Such refractories have presented many advantages in certain uses over the older type of refractory products which comprise granular heat-resistant materials bonded in desired shapes with other heat-resistant ceramic materials. Some fused cast refractories resisted attack by corrosive melts such as glass and molten metal oxides. Such corrosion resistance was not, however, as good as desired.
Many different compositions for fused cast refractories have been previously suggested. Such fused cast refractories are, for example, suggested in U.S. Pat. Nos. 2,063,154; 2,279,260; 2,911,313; 3,188,219; 3,232,776; 3,759,728; 3,773,531 and 4,158,569.
Unfortunately, such fused cast refractories of the prior art, even when they contained chromia (Cr.sub.2 O.sub.3) in amounts in excess of 65 weight percent, were subjected to unacceptable corrosion and stoning effects from certain corrosive glasses such as "E" glass as previously described.
Even when attempts were specifically made to reduce such corrosion and stoning by increasing chromia content, as described in U.S. Pat. No. 3,759,728, corrosion resistance was not as high as desired.
Some success was obtained when certain sintered ceramics were used in contact with corrosive melts such as "E" glass; however, even sintered compositions were not as good as desired and furthermore the manufacture of acceptable sinters is difficult and costly. In addition, sinters generally have an undesirably high porosity.